This invention relates to magnetic separators in general, and more particularly to an improved separator which may be efficiently operated. Magnetic separators are known in which a mixture of particles having different magnetic susceptibilities, (magnetic susceptibilities will hereandafter be designated by the symbol (k)), is led continuously through the field of a stationary superconducting magnet arrangement and subjected to the influence of the product of the induction B and its local field gradient grad B. In such an arrangement, particles of a given susceptibility are continuously separated magnetically from the mixture by means of a carrier running through the magnetic field and are removed from the carrier outside the influence of the magnetic field.
One such separator of this type is described in U.S. Pat. No. 3,503,504 and comprises a sector-shaped magnet arrangement consisting of a multiplicity of small, superconducting magnet coils which are arranged beside each other and which are alternately excited in one and the other direction in order to generate the needed field gradients. Around the magnet arrangement a closed hollow cylinder of hard rubber or non-magnetic steel coated with hard rubber and which acts as the carrier rotates at a close axial distance. The carrier also encloses the cryostat of the superconducting magnet arrangement with it in turn surrounded by a stationary, hollow, cylindrical housing with an inlet for the mixture and separate outlets located underneath for the magnetic particles which have been separated and for the other components of the mixture. Although it is indicated that magnet coils field strengths of 3.5 tesla are attainable in the immediate vicinity of the magnet coils, only 0.7 tesla are at most available at the separation region itself, i.e., outside the wall of the carrier. This is no more than that in previously known electromagnetic separators such as that of U.S. Pat. No. 3,289,836. In electromagnetic separators of that type, a large number of small electromagnets are placed along a conveyor and separation arrangement for the mixture with the electromagnets continuously moved at constant spacings along the separation device. Clearly, such an arrangement is expensive since a large separator of electromagnets and heavy complicated support and handling devices along with flushing devices are required. The attraction force F = k. B.grad B on magnetizable particles, which are attainable with known superconducting or electromagnetic separators, are sufficient only for separating ores which have a relative high magnetizability. Such ores are essentially ferromagnetic ores such as magnetite and hematite. Non-ferromagnetic ores having smaller susceptibilities cannot be handled at all with these magnetic separators. If, for example, magnetite and hematite are to be extracted separately from a mixture when using the prior art devices, than either a magnetic separator with a product of induction and field gradient tuned to the susceptibility of magnetite and a second magnetic separator following the first on the transport path, having a higher attraction force tuned to hematite are required, or alternatively, the mixture must be run through the magnetic separator twice, after the excitation of the latter has been suitably increased. For a large number of particles of different susceptibility, correspondingly larger numbers of separators or repeated runs with changed excitation are required.
Thus, it can be seen that there is a need to generate high inductions and field gradients at a lower cost in such magnet arrangements as well as keeping the carriers and separation devices simple while maintaining continuous-throughput operation with satisfactory separation of even relatively weakly magnetizable particles, and to be able to sort the different components according to their susceptibility.